BY C. W. DE VIS, M.A. 185 
development of a ridge descending forwards upon the angular 
from the outer tubercle of the surangular; commencing with 
that tubercle, which itself is of much greater size than in a large 
C. porosus, it forms a continuous and nearly smooth boundary 
to the deeply sculptured surface of the surangular: subsiding 
as it approaches the angular-surangular suture it immediately 
recommences below it, and at about half of its course, inter- 
rupted by the fracture of the bone, it attains a height of twenty- 
five mm. above the general level. This ridge is but faintly 
marked in the adult C. porosus. On the other hand, the 
sinuous groove conspicuous in the latter reptile below the ridge 
is in the fossil scarcely observable. Neither ridge nor groove is 
present in the feebler species of the fresh water. 
The angular-surangular suture preserves a straight course 
without any flexures. The upper surface of the surangular is 
28mm. in breadth (in another example 37mm.), flat and 
angular on both edges, the angularity increasing with age. 
The hinder part of its inner edge, however, rises into a low 
elongated tubercle which adds to the depth of the antero- 
exterior wall of the articular cavity. Apart from such increase 
the cavity is deeper than in crocodilus. The posterior lip of the 
articular cavity, of which about half is preserved, is nearly 
straight and level; the buttress behind it rising from the 
articular slopes gradually and equably towards the nearly flat, 
upper and posterior surface of the bone without forming on its 
exterior angle a strong convexity, dipping suddenly into as 
strong a concavity, behind it as in C. porosus, or developing 
more than a faint trace of the mesial ridge which, in the latter, 
separates the outer from the inner tracts of the articular. From 
the outer tubercle of the surangular its posterior edge descends 
rapidly, so that, at the fracture of the bone, it is reduced to a 
depth of 14mm.; on the inner surface of the fossil the angular- 
surangular suture is seen descending forwards with a very 
oblique course. 
